Force limiting mechanism for prosthetic heart valve delivery apparatus

Abstract

A medical assembly can include a radially expandable prosthetic heart valve and a delivery apparatus. The delivery apparatus can include a handle, an actuation member, and a force limiting mechanism within the handle including a pivot arm coupled to a base portion. The actuation member can apply a proximally directed force to the prosthetic valve to cause the valve to expand. The actuation member can be coupled to the pivot arm such that a force applied to the actuation member causes the pivot arm to pivot. The force limiting mechanism can pinch the actuation member between the pivot arm and the base portion when the force applied to the actuation member exceeds a predetermined force to prevent proximal movement of the actuation member and can allow proximal movement of the actuation member to produce radial expansion of the prosthetic valve when the force applied is less than the predetermined force.

We claim: 
     
       1. A medical assembly comprising:
 a prosthetic heart valve that is radially expandable and compressible between a radially compressed configuration and a radially expanded configuration; and 
 a delivery apparatus comprising:
 a handle; 
 at least one actuation member extending from the handle and coupled to the prosthetic heart valve, wherein the at least one actuation member is configured to apply a proximally directed force to the prosthetic heart valve to cause the prosthetic heart valve to foreshorten axially and expand radially; and 
 a force limiting mechanism positioned within the handle and comprising a pivot arm and a base portion, wherein the pivot arm is pivotably coupled to the base portion, wherein the actuation member is movably coupled to the pivot arm such that a force applied to the actuation member causes the pivot arm to pivot relative to the base portion; 
 wherein the force limiting mechanism is configured to pinch the at least one actuation member between the pivot arm and the base portion when the force applied to the at least one actuation member exceeds a predetermined force, thereby preventing proximal movement of the at least one actuation member, and wherein the force limiting mechanism permits proximal movement of the at least one actuation member to produce radial expansion of the prosthetic heart valve when the force applied to the at least one actuation member is less than the predetermined force. 
 
 
     
     
       2. The medical assembly of  claim 1 , wherein the at least one actuation member extends around a pulley mounted on the pivot arm, wherein the pulley can pivot with the pivot arm upon application of the force to the at least one actuation member, and wherein the at least one actuation member extends between the pivot arm and the base portion. 
     
     
       3. The medical assembly of  claim 2 , wherein the pulley comprises a first pulley and the at least one actuation member further extends around a second pulley coupled to the handle and spaced from the pivot arm, the second pulley positioned proximal to the pivot arm, and wherein the base portion is connected to a first side of the handle and the second pulley is connected to a second side of the handle, the second side opposite the first side. 
     
     
       4. The medical assembly of  claim 1 , wherein the force limiting mechanism further comprises a biasing member configured to exert a biasing force against the pivot arm, wherein the biasing force is selected such that:
 when the force applied to the at least one actuation member is less than the predetermined force, the pivot arm is prevented from pivoting relative to the base portion, against the biasing force; and 
 when the force applied to the at least one actuation member exceeds the predetermined force, the pivot arm pivots relative to the base portion. 
 
     
     
       5. The medical assembly of  claim 4 , wherein the biasing member comprises a spring that is linearly expandable between a compressed configuration and an expanded configuration, wherein one end portion of the spring is coupled to the pivot arm, wherein another end portion of the spring is coupled to the handle, and wherein the spring is configured such that a proximally directed force applied to the at least one actuation member causes an expansion force to be applied to the spring. 
     
     
       6. The medical assembly of  claim 4 , further comprising an adjustment mechanism configured to adjust the predetermined force, and wherein the adjustment mechanism comprises an adjustment screw comprising a threaded portion that extends through the handle and is coupled to the biasing member. 
     
     
       7. The medical assembly of  claim 6 , wherein the adjustment screw further comprises a screw head coupled to the threaded portion, the screw head arranged outside of the handle, wherein the handle includes an internally threaded portion secured to an internal surface of the handle, the internally threaded portion having an internally threaded surface configured to engage with the threaded portion of the adjustment screw, wherein the adjustment screw is rotatable in a first direction which moves the adjustment screw further outside of the handle, pre-expands the biasing member, and increases the predetermined force, and wherein the adjustment screw is rotatable in a second direction, opposite the first direction, which moves the adjustment screw into the handle and toward the pivot arm, moves the biasing member to a more relaxed state or a fully relaxed state, and decreases the predetermined force. 
     
     
       8. The medical assembly of  claim 4 , wherein the pivot arm is pivotably coupled to the base portion by a pivot element extending through a first end portion of the pivot arm and the base portion, further comprising an adjustment mechanism configured to adjust the predetermined force, and wherein the adjustment mechanism comprises a sliding element arranged within the pivot arm and coupled to the pivot element, the pivot element arranged within an elongate slot extending from the first end portion of the pivot arm, toward a second end portion of the pivot arm, the pivot element configured to slide along the slot in response to movement of the sliding element within the pivot arm, where a position of the pivot element determines a pivot point of the pivot arm and an arc length through which the pivot arm pivots in order to pinch the actuation member. 
     
     
       9. The medical assembly of  claim 1 , wherein the actuation member is one of a flexible cable, a suture, a wire, a cord, a flexible rod, and a flexible shaft. 
     
     
       10. A delivery apparatus for an implantable medical device comprising
 a handle; 
 at least one actuation member extending from the handle and coupled to the medical device, wherein the at least one actuation member is configured to apply a proximally directed force to the medical device; and 
 a force limiting mechanism arranged within the handle, the force liming mechanism comprising a pivot arm configured to limit an amount of the proximally directed force that can be applied by the at least one actuation member to the medical device. 
 
     
     
       11. The delivery apparatus of  claim 10 , wherein the pivot arm is configured to prevent the at least one actuation member from applying a proximally directed force to the medical device if a proximally directed force greater than a predetermined threshold is applied to the at least one actuation member, wherein the force limiting mechanism further comprises a base portion, and wherein the pivot arm is configured to pivot and retain the at least one actuation member between the pivot arm and the base portion if a proximally directed force greater than the predetermined threshold is applied to the at least one actuation member. 
     
     
       12. The delivery apparatus of  claim 11 , wherein the force limiting mechanism further comprises a biasing member configured to exert a biasing force against the pivot arm and prevent pivoting of the pivot arm if the proximally directed force applied to the at least one actuation member is less than the predetermined threshold and permit pivoting of the pivot arm if the proximally directed force applied to the at least one actuation member exceeds the predetermined threshold. 
     
     
       13. The delivery apparatus of  claim 12 , wherein the biasing member comprises a spring. 
     
     
       14. The delivery apparatus of  claim 12 , wherein the force limiting mechanism further comprises an adjustment screw including a threaded portion in threaded engagement with an internally threaded portion of the handle, where a first end of the threaded portion is coupled to the biasing member and a second end of the threaded portion is configured to be rotated in a first direction that increases the biasing force and an opposite, second direction that decreases the biasing force. 
     
     
       15. The delivery apparatus of  claim 12 , wherein the pivot arm includes an adjustable pivot element about which the pivot arm pivots relative to the base portion, and wherein the pivot element is configured to slide within an elongated slot of the pivot arm extending from a first end portion toward a second end portion of the pivot arm, in response to linear translation of a sliding element coupled to the pivot element and in sliding engagement with a portion of the pivot arm, in order to adjust a position of a pivot point of the pivot arm. 
     
     
       16. The delivery apparatus of  claim 10 , wherein the force limiting mechanism further comprises a pulley mounted on the pivot arm and the at least one actuation member is routed at least partially around the pulley. 
     
     
       17. The delivery apparatus of  claim 10 , wherein the at least one actuation member is configured to produce radial expansion of the medical device upon application of the proximally directed force to the at least one actuation member, wherein the medical device is a mechanically expandable prosthetic heart valve including a plurality of interconnected struts, and wherein the struts are pivotably coupled to one another at one or more pivot joints arranged along a length of each strut. 
     
     
       18. A method of implanting a prosthetic heart valve, comprising:
 inserting into a body of a patient a distal end portion of a delivery apparatus and a prosthetic heart valve coupled to the distal end portion of the delivery apparatus in a radially compressed configuration, the delivery apparatus comprising:
 a handle; 
 at least one actuation member extending from the handle and coupled to the prosthetic heart valve and configured to apply a proximally directed force to the prosthetic heart valve to cause the prosthetic heart valve to foreshorten axially and expand radially; and 
 a force limiting mechanism configured to limit an amount of the proximally directed force that can be applied by the at least one actuation member to the prosthetic heart valve; 
 
 advancing the delivery apparatus distally until the prosthetic heart valve is disposed at a selected implantation site; and 
 radially expanding the prosthetic heart valve by applying a proximally directed force to the at least one actuation member so as to move the at least one actuation member relative to the force limiting mechanism. 
 
     
     
       19. The method of  claim 18 , further comprising, when the proximally directed force applied to the at least one actuation member exceeds a predetermined force during the radially expanding the prosthetic heart valve, arresting movement of the at least one actuation member with the force limiting mechanism and stopping radially expanding the prosthetic heart valve, and wherein arresting movement of the at least one actuation member with the force limiting mechanism includes pivoting a first end portion of a pivot arm of the force limiting mechanism into engagement with the at least one actuation member and pinching the at least one actuation member between the first end portion and a base portion of the force liming mechanism to which the pivot arm is coupled. 
     
     
       20. The method of  claim 19 , further comprising, in response to the proximally directed force applied to the at least one actuation member exceeding the predetermined force, decreasing an amount of the proximally directed force applied to the at least one actuation member so that it is less than the predetermined force, and then further moving the at least one actuation member relative to the force limiting mechanism, and wherein further moving the at least one actuation member relative to the force limiting mechanism includes moving the first end portion of the pivot arm out of engagement with the at least one actuation member and allowing the at least one actuation member to slide relative to the pivot arm.